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 Pro/Engineer   September 2001   Tip-of-the-Month
Centerlines of Arcs in X-Sections
(for revolved arcs, and swept arcs, etc.)

Q:  How can you show the center of an arc in a drawing cross section if the arc is part of a revolve or a sweep?
 Figure 1

A:  You can't, directly.

However, there is a work around.  If you need an axis at the center of an arc in a position that Pro/E will typically not allow just create the axis independently.

The example for this Tip-of-the-month is shown in Figure 1.  The question is how to show an axis at the center of the revolved arc?  For simplicity, the 2 desired axes are shown in Magenta in Figure 3 below.

- One solution is to sketch them in at the drawing level.  The problem with that is they are not parametric, so they don't move with the model.

- A second, more robust method is to put the axis in the model.  The following steps demonstrate the technique.
 Figure 2

1. Create a datum plane through the part at the area of concern.  This will usually be the datum for the x-section.

2.
3. Create a datum curve as an intersection of surfaces to define the arc location.  This is done using  Feature > Create > Datum > Curve (or use the datum curve icon in 2001) > Intr. Surfs.  Select Whole and select the datum plane of step 1, then select Whole and select a surface of the solid.  The curve will go in as shown in Figure 2.  (Note: the red and green segments are highlighted separately.)

4.
5. Create a datum point at the center of the desired arc.  Use Feature > Create > Datum > Point (or use the datum point icon in 2001) > At Center then pick the desired arc segment of the curve -- the red or green segment in Figure 2.  (Note:  Watch the messages.  If the segment is not an arc, Pro/E will not place the point -- and for that matter, if it's not really an arc, you don't want an axis for it in the drawing.  If it is really supposed to be an arc, examine the geometry and be sure the datum plane is perpendicular as expected.)

6.
7. Place an axis through the point.  Use Feature > Create > Datum > Axis (or use the datum axis icon in 2001) > Pnt Norm Pln.  Select the plane then the point.  Figure 2 shows points and axes placed for both the highlighted arcs in the revolved protrusion.
 Figure 3

The resulting axis can now be used in the drawing.

Use Detail > Show / Erase > Show (or use View > Show and Erase... in 2001) then select the axis button and Show All or select the specific axis.  The result can be as shown for our example in Figure 3.  The Magenta color added for emphasis.

Have a Wonderful Day!
See you next month.

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